Rapid evolution and the cost of resistance toBacillus thuringiensisin greenhouse populations of cabbage loopers,Trichoplusia ni

Abstract

The microbial insecticide Bacillus thuringiensis (Bt) has become the mainstay of non-chemical control of Lepidopteran pests, either as sprays or through the incorporation of Bt toxins into transgenic crops. Given the wide use of Bt, it is striking that currently only one pest species, Plutella xylostella, has been reported to have developed significant resistance to Bt outside the laboratory. By contrast, we report here the frequent and rapid development of resistance to B. thuringiensis kurstaki (Dipel, Abbott) in populations of cabbage loopers, Trichoplusia ni, in commercial greenhouses. Resistance to Bt appears to be costly and there is a rapid decline of resistance in populations collected from greenhouses and maintained in the laboratory without selection. Management of pests resistant to Bt in vegetable greenhouses will require sporadic use of Bt-based sprays or alternatively use of sprays containing other Bt toxins.

Frequency and fitness cost of resistance to Bacillus thuringiensis in Chrysomela tremulae (Coleoptera: Chrysomelidae)

“…A decrease in resistance to Bt in Bt-free environments has already been reported in laboratory strains of several pests (McGaughey and Beeman, 1988;Tabashnik et al, 1991;Janmaat and Myers, 2003). Unfortunately, the genetic basis of the resistance selected in these strains was generally unknown, as resistance ratio variation is generally investigated by assessing changes in LC 50 , and little attention was paid to the possible effects of genetic drift.…”

“…For example, Hawaiian populations of P. xylostella were treated with Bt and Bt cotton fields were planted in Arizona some years before collection of the P. gossypiella populations in which Bt resistance were detected. Similarly, the high level of Bt resistance discovered by Janmaat and Myers (2003) in greenhouse populations of cabbage loopers, Trichoplusia ni, probably resulted from the massive treatment of this pest with Bt toxins. Conversely, populations of C. tremulae have never been exposed to any particular Génissel et al (2003a), q 1 , and that estimated here, q 2 .…”

“…Indeed, if resistance entails a fitness cost, the spread of a recessive allele could be prevented by an appropriate resistance management strategy (Lenormand and Raymond, 1998;Carrière and Tabashnik, 2001;Carrière et al, 2004;Bates et al, 2005). Although fitness costs associated with Bt resistance were not always detected (eg Gould and Anderson, 1991;Tang et al 1997), they have been reported in many pests (Groeters et al, 1994;Trisyono and Whalon, 1997;Alyokhin and Ferro, 1999;Oppert et al, 2000;Carrière et al, 2001a, b;Akhurst et al, 2003;Janmaat and Myers, 2003;Higginson et al, 2005. Bird and Akhurst (2004 showed that, in H. armigera, most fitness costs associated with Bt resistance (eg a lower percentage of survival or a longer mean time to pupation) are recessive.…”

Delayed resistance to transgenic cotton in pink bollworm

“…Although field-evolved resistance to Bt crops has not yet been documented, resistance to Bt toxins has evolved in laboratory-selected strains of many insects (2,5,6). Furthermore, resistance to Bt sprays has evolved in greenhouse populations of cabbage looper (Trichoplusia ni) and in field populations of diamondback moth (Plutella xylostella) (2,5,6,10).…”

A single major QTL controls expression of larval Cry1F resistance trait in Ostrinia nubilalis (Lepidoptera: Crambidae) and is independent of midgut receptor genes

“…Although not an equivalent representation of field conditions due to reductions in effective population sizes and exposure to initial low toxicity environments (Harshman and Hoffmann 2000), laboratory selections show that target insects have the genetic potential for developing Bt resistant phenotypes (Ferré and Van Rie 2002). Realization of this genetic potential was shown via emergence of populations that are resistant to field-exposed levels of foliar or transgenic Bt toxins, and include species Plodia interpunctella (McGaughey 1985), Plutella xylostela (Tabashnik et al 1990), Tricoplusia ni (Janmaat and Myers 2003), Busseola fusca (van Rensburg 2007), and Spodoptera frugiperda (Matten et al 2008). Although significant levels of field damage have not been reported, Tabashnik (2008) suggest resistance to GE cotton expressing Cry1Ac toxin has emerged in Helicoverpa zea populations based on analysis of more than a decade of phenotypic monitoring data.…”